Ballast water is taken on by ships in order to attain a more stable position in the water with a small cargo. For this purpose ballast tanks are provided, into which, at the departure port before a journey with small cargo, seawater is pumped directly from the harbour. With this taking on of ballast water, organisms are also taken on, which are conveyed on the voyage in the ballast tank. The water taken on undergoes only coarse filtering.
In the destination port the ballast water is then discharged in order to re-establish the full loading capacity of the vessel once more. The ballast water is then pumped out of the tanks into the surrounding water when outside or in the destination port. Because the departure port and the destination port form different ecosystems, especially with overseas voyages, the risk should be avoided of the organisms taken up with the ballast water being discharged into the foreign ecosystem. To achieve this, the ballast water is disinfected when taken on and/or when being discharged.
According to the prior art, the disinfection device is incorporated in the pump line, specifically with disinfection by UV radiation sources in the form of radiation units aligned transversely to the direction of flow. The radiation units are in this situation either arranged one behind another in one plane in the direction of flow, or in two planes, likewise one behind another in the direction of flow but arranged offset against the mid-axis of the pipe at a distance from one another. A further variant is known in which numerous UV radiators are arranged in two planes parallel to the mid-axis of the pipe, but are aligned at an angle to the direction of flow. In this way a greater radiation length can be used with a given diameter of the pipe.